Hybrid drive assembly for a vehicle, in particular a scooter

ABSTRACT

A hybrid drive assembly ( 1 ) for a vehicle having at least one drive wheel ( 2 ), the drive assembly including an internal combustion engine ( 3 ); a transmission unit ( 5 ) interposed between a drive shaft ( 4 ) of the internal combustion engine ( 3 ) and a propeller shaft ( 6 ) connected angularly to the drive wheel ( 2 ), and in turn including a continuously variable transmission ( 7 ) having a drive pulley ( 10 ) connected angularly to the drive shaft ( 4 ) and a driven pulley ( 11 ), and a centrifugal clutch ( 8 ) having a hub ( 20 ) connected to the driven pulley, and a driven bell ( 26 ) connected to the propeller shaft ( 6 ); and an electric machine ( 32 ) having a rotor ( 35 ) integral with the bell ( 26 ) of the centrifugal clutch ( 8 ). The drive assembly ( 1 ) is controlled by a control unit ( 38 ), in response to a number of input signals (Ss, Sa, Sf), in a number of operating modes including an all-combustion propulsion mode, an all-electric propulsion mode, a first hybrid propulsion mode wherein the internal combustion engine ( 3 ) and the electric machine ( 32 ) are connected in series, and a second hybrid propulsion mode wherein the internal combustion engine ( 3 ) and the electric machine ( 32 ) are connected in parallel.

TECHNICAL FIELD

The present invention relates to a hybrid drive assembly for a roadvehicle, in particular a scooter.

BACKGROUND ART

As is known, numerous road vehicle, in particular car, manufacturers arecurrently experimenting hybrid-propulsion vehicles, some of which haverecently been marketed. Though “hybrid propulsion” normally refers tothe use of two or more different propulsion systems, the solutionshitherto proposed are normally a combination of an internal combustionengine (hereinafter referred to simply as a “combustion engine”) and anelectric motor, to exploit the advantages and compensate thedisadvantages of each.

More specifically, the main advantage of a combustion engine, and thereason why it is used almost exclusively in road vehicles, is the fueldistance obtainable by virtue of the high energy concentration of thefuel employed (substantially hydrocarbons). On the other hand, acombustion engine produces harmful emissions, can only operate within agiven speed range, thus requiring the use of auxiliary components(gearbox and clutch), and has a relatively high noise level.

Moreover, even within the operating range, the efficiency of acombustion engine is fairly low (about 20-30%), and variations in thesteady-state operation of the engine considerably increase pollutantemissions.

An electric motor produces no “local” pollution, is quiet, highlyefficient (about 80%), and capable of generating torque as of start-up.Application in road vehicles, however, has so far been impaired by thelimited range of the electric batteries currently available, at leastthose of a size, weight and cost feasible for earth vehicles.

To eliminate or reduce the drawbacks associated with the use of one typeof engine/motor, hybrid solutions of various configurations have beenproposed enabling alternative or combined use of both propulsionsystems.

More specifically, in a first known so-called “series hybrid”combination, the combustion engine serves solely to drive an electriccurrent generator, which charges the batteries powering the electricmotor: propulsion is therefore governed exclusively by the electricmotor. This solution provides for a considerable reduction inconsumption, by the combustion engine only being called upon to supplyaverage power, and so being operating in optimum steady conditions.

In the “parallel hybrid” configuration, both the combustion engine andthe electric motor are connected to the drive wheels by appropriatetransmission mechanisms.

Known hybrid drive assemblies of the type briefly described above arecomplex, expensive, and bulky, which is why, to the Applicant'sknowledge, they have never been marketed for compact, low-cost vehicles,such as scooters.

EP-A-0 908 343 discloses a hybrid drive assembly including an internalcombustion engine having a drive shaft, an electric machine having arotor connected to a primary shaft aligned to the engine drive shaft, aclutch interposed between the engine drive shaft and the electricmachine rotor, and a transmission unit including a CVT interposedbetween the primary shaft and the wheel axle.

Besides being considerably complex and thus not adapted for use in smallroad vehicles such as scooters, the above-referenced known hybrid driveassembly has a drawback in that the electric machine is located upstreamfrom the transmission unit, and in particular the CVT, so that, when theelectric machines operates as a generator (regenerative brake), energyrecovery efficiency is reduced.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide an extremelystraightforward, low-cost, compact hybrid drive assembly, which can alsobe used in small, low-cost road vehicles, such as scooters, but whichalso permits selection of a number of operating modes on the basis ofdifferent operating requirements or road conditions.

According to the present invention, there is provided a hybrid driveassembly for a vehicle having at least one drive wheel, the driveassembly comprising an internal combustion engine; and a transmissionunit interposed between a drive shaft of the internal combustion engineand a propeller shaft connected angularly to the drive wheel, and inturn comprising a clutch and a transmission having a drive elementconnected angularly to the drive shaft of the internal combustion engineand a driven element connectable to said propeller shaft; the driveassembly further including an electric machine which can be operatedinstead of or in combination with said internal combustion engine,characterised in that said clutch is interposed between said drivenelement of said transmission and said propeller shaft, and has a drivemember connectable to said driven element of said transmission and adriven member connected to the propeller shaft, said electric machinecomprising a rotor connected angularly and permanently to said drivenmember of said clutch.

The present invention also relates to a vehicle, in particular ascooter, comprising such a hybrid drive assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Two preferred, non-limiting embodiments of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1 shows a diagram of a hybrid drive assembly in accordance with afirst embodiment of the invention;

FIG. 2 shows a diagram of a control system for controlling the FIG. 1drive assembly;

FIG. 3 shows a partial diagram of an alternative embodiment of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in FIG. 1 indicates as a whole a hybrid drive assembly for ascooter having a rear drive wheel 2 of axis A.

Drive assembly 1 comprises a combustion engine 3 having a drive shaft 4of axis B parallel to axis A; and a transmission unit 5 interposedbetween drive shaft 4 and a propeller shaft 6 of axis C, parallel toaxes A and B, and connected angularly to the drive wheel 2.

More specifically, transmission unit 5 comprises a continuously variabletransmission or CVT 7 (hereinafter referred to simply as “CVT 7”), and acentrifugal clutch 8 in series with each other.

CVT 7 comprises a drive pulley 10 fitted to drive shaft 4; a drivenpulley 11 coaxial with and fitted in angularly free manner to propellershaft 6; and a V belt 12 looped about pulleys 10, 11. Pulleys 10, 11have respective V grooves 13, 14 for belt 12, and are defined by twohalf-pulleys 10 a, 10 b and 11 a, 11 b respectively, which are movableaxially with respect to each other to vary the width of groove 13, 14and therefore the winding diameter of belt 12.

Variation of the relative axial position of half-pulleys 10 a, 10 b ofdrive pulley 10 is controlled by a known centrifugal device not shown;and half-pulleys 11 a, 11 b of driven pulley 11 are loaded axiallytowards each other by a spring 15 to automatically adapt the windingdiameter of belt 12 inversely to that of drive pulley 10.

More specifically, driven pulley 11 is connectable selectively topropeller shaft 6 by centrifugal clutch 8, which comprises a hub 20fitted for rotation to driven pulley 11; a number of centrifugal weights21 carried by hub 20 and maintained in a radially withdrawn restposition by springs 22; and a driven bell 26 integral with propellershaft 6.

In response to rotation of hub 20 at an angular speed sufficient toovercome the reaction of springs 22, centrifugal weights 21 moveradially outwards to cooperate frictionally with a substantiallycylindrical lateral wall 25 of bell 26.

Spring 15 of driven pulley 11 is compressed axially between hub 20 ofcentrifugal clutch 8 and the movable half-pulley 11 b, so as to loadhalf-pulley 11 b axially towards the fixed half-pulley 11 a.

Propeller shaft 6 is connected to drive wheel 2 by a conventionalreduction gear 28 shown only schematically in FIG. 1 and havingpropeller shaft 6 as the input member, and, as the output member, ashaft 29 of axis A, to which drive wheel 2 is fixed rigidly in use.

According to the present invention, drive assembly 1 also comprises anelectric machine 32 coaxial with centrifugal clutch 8 and having astator 33 housed in a fixed casing 34 of drive assembly 1, and a rotor35 outwardly coaxial with lateral wall 25 of bell 26 of centrifugalclutch 8, and integral with bell 26 and therefore with propeller shaft6.

Electric machine 32 is conveniently a reversible type, and is connectedto the vehicle battery 36 (FIG. 2) for use as a generator to charge thebattery in given operating conditions. Drive assembly 1 also comprisesan electric generator 37 driven by combustion engine 3 in known mannerand connected to battery 36.

Drive assembly 1 is controlled by a control unit 38 which controlselectric machine 32, and an actuator 39 for adjusting the position of abutterfly valve 40 of combustion engine 3, in response to a number ofinput signals indicating the operating conditions of assembly 1, andwhich comprise a signal Sa indicating the position of an acceleratorgrip 44, and signals Sf indicating user action on the brake levers 45.

Control unit 38 also receives input signals Ss from a selector device 46located on the instrument panel of the vehicle and for selecting theoperating mode of drive assembly 1. The selector device may comprise,for example, a number of buttons T, E, P, S for respectively selectingthe following operating modes:

“combustion” (T), in which propulsion is provided solely by combustionengine 3;

“electric” (E), in which propulsion is provided solely by electricmachine 32 operating as an electric motor;

“parallel hybrid” (P), in which combustion engine 3 and electric machine32 both provide drive power; and

“series hybrid” (S), in which combustion engine 3 is used solely topower electric generator 37 to charge battery 36, while torque to thedrive wheel is provided solely by electric machine 32.

Operation of drive assembly 1 will now be described with reference tothe above operating modes.

In “combustion” mode, electric machine 32 is not powered, so that,disregarding the slight increase in the moment of inertia of bell 26 ofcentrifugal clutch 8, drive assembly 1 functions in exactly the same wayas a conventional, all-mechanical assembly, as though electric machine32 did not exist. More specifically, at idling speed of combustionengine 3, CVT 7 maintains a “short” ratio defined by the minimum windingdiameter of belt 12 on drive pulley 10, and by the maximum windingdiameter of belt 12 on driven pulley 11. In this condition, centrifugalclutch 8 is open, so that propeller shaft 6 is disconnected from CVT 7and transmits no torque to drive wheel 2.

As the rotation speed of drive shaft 4 increases, centrifugal clutch 8is closed by the movement of centrifugal weights 21, which rotationallyconnect bell 26, and therefore propeller shaft 6, to driven pulley 11 ofCVT 7, so that the vehicle is started with a “short” transmission ratio.

As the speed of drive shaft 4 increases further, CVT 7 switches,gradually and automatically in known manner not described in detail,from said “short” ratio to a “long” ratio defined by the maximum windingdiameter of belt 12 on drive pulley 10, and by the minimum windingdiameter of belt 12 on driven pulley 11.

When decelerating or braking, the above operating steps are repeated inreverse. Moreover, rotor 35 of electric machine 32, being integral withbell 26 of the centrifugal clutch, is driven by drive wheel 2, so thatelectric machine 32 acts as an electric current generator which drawsmechanical power (and so acts as an electrodynamic brake) and generateselectrical power.

In “electric” mode, combustion engine 3 is not operated, so that driveshaft 4 and CVT 7 are stationary, and centrifugal clutch 8 is open, bycentrifugal weights 21 being subjected solely to the return forceexerted by springs 22. Everything upstream from bell 26, includingcombustion engine 3 and CVT 7, is therefore completely disconnected fromdrive wheel 2.

The drive torque of electric machine 32, whose rotor 35 is integral withbell 26, is transmitted by the bell directly to propeller shaft 6 andvia reduction gear 28 to drive wheel 2.

In this operating mode too, when decelerating or braking, with no powerbeing generated by electric machine 32, rotor 35 is driven and electricmachine 32 draws mechanical power and generates electrical power tocharge battery 36.

In “parallel hybrid” mode, combustion engine 3 and electric machine 32,the latter operating as a motor as described in “electric” mode, operatesimultaneously; and the torque and power produced by both come togetherand are added at propeller shaft 6, thus greatly improving performance.Moreover, user power demand can be divided between combustion engine 3and electric machine 32 to reduce consumption and/or emissions.

In “series hybrid” mode, combustion engine 3 serves solely to driveelectric generator 37, and propulsion is provided solely by electricmachine 32. With the architecture of assembly 1 shown in FIG. 1, forcombustion engine 3 to be disconnected from drive wheel 2, engine speedmust be low enough not to close centrifugal clutch 8. In the event thisimposes a less than optimum operating condition of combustion engine 3in terms of efficiency and emissions, the architecture of assembly 1 isappropriately modified as shown in FIG. 3, in which driven pulley 11 andhub 20 of the centrifugal clutch, as opposed to being connectedpermanently, are connectable selectively by a coupling 51, e.g. anelectromagnetic so-called “Gravina coupling” controlled by unit 38.

With this transmission arrangement, when “series hybrid” mode isselected, coupling 51 is set to the “open” position, so that combustionengine 3 can operate at constant speed selected to optimize efficiencyand minimize emissions, regardless of the intervention threshold speedof centrifugal clutch 8. Control unit 38 may conveniently be programmedto operate combustion engine 3 at two or more different power levels(but always at constant speed at each power level) depending on the meanpower required by the user and/or road conditions.

Moreover, coupling 51 permits switching from one operating mode toanother without stopping the vehicle.

When braking or decelerating in hybrid modes too, electric machine 32acts as a generator, as opposed to a motor, and therefore as aregenerative brake.

The advantages of drive assembly 1 according to the present inventionwill be clear from the foregoing description.

In particular, the transmission architecture provides for obtaining anextremely straightforward, low-cost, compact hybrid drive assembly thatcan also be used in small, low-cost road vehicles such as scooters, andwhich can operate in a number of modes selectable on the basis ofdifferent operating requirements and road conditions.

Moreover, the various operating modes permit energy saving, by virtue ofelectric machine 32 operating as a regenerative brake.

Finally, the transmission architecture provides for optimum globalefficiency in each operating mode, by limiting undesired interactionbetween the two propulsion systems when operated individually, and bysynergistically exploiting the potential of both in hybrid operatingmodes. In fact, in “combustion” mode, assembly 1 operates as thoughelectric machine 32 did not exist; in “electric” mode, combustion engine3 and CVT 7 are disconnected from drive wheel 2 and in no way impairefficiency; in “parallel hybrid” mode, the total power of bothpropulsion systems can be exploited, and power demand divided betweenthe two propulsion systems to reduce consumption and/or emissions; and,in “series hybrid” mode, considerable energy saving is achieved byoperating combustion engine 3 in optimum steady conditions in terms ofefficiency.

Clearly, changes may be made to, and to control of, drive assembly 1 asdescribed herein without, however, departing from the scope of theaccompanying claims.

In particular, CVT 7 may be replaced by a different type oftransmission, e.g. a synchronous belt transmission; centrifugal clutch 8may be replaced by a controlled clutch; and electric machine 32 may belocated differently, providing rotor 35 is permanently connecteddownstream from clutch 8, i.e. connected permanently to drive wheel 2.

One or more “automatic” control modes may be provided, in which thecontrol unit, as opposed to activating the above control modes(“combustion”, “electric”, “parallel hybrid” and “series hybrid”) asselected by the user, may switch automatically from one to another onthe basis of programmed control logic, e.g. to optimize performance,minimize consumption or emissions, or in particular operatingconditions. For example, an automatic switch may be made from “electric”to “combustion” or “series hybrid” mode, in the event the charge ofbattery 36 falls below a predetermined threshold value.

1. A hybrid drive assembly for a vehicle having at least one drivewheel, the drive assembly comprising an internal combustion engine; anda transmission unit interposed between a drive shaft of the internalcombustion engine and a propeller shaft connected angularly to the drivewheel, and in turn comprising a clutch and a transmission, having adrive element connected angularly to the drive shaft of the internalcombustion engine and a driven pulley connectable to said propellershaft; the drive assembly further including an electric machine whichcan be operated instead of or in combination with said internalcombustion engine, characterized in that said clutch is interposedbetween said driven pulley of said transmission and said propellershaft, and has a drive member connectable to said driven pulley of saidtransmission and a driven member connected to the propeller shaft, saidelectric machine comprising a rotor connected angularly and permanentlyto said driven member of said clutch and having a coupling interposedbetween said driven pulley and said drive member of said clutch.
 2. Adrive assembly as claimed in claim 1, characterized in that saidtransmission is a CVT, said drive element consists of a drive pulley. 3.A drive assembly as claimed in claim 1, characterized in that saidclutch is a centrifugal clutch; said driven member of said clutch beinga bell integral with said propeller shaft.
 4. A drive assembly asclaimed in claim 3, characterized in that said rotor of said electricmachine is coaxial and integral with said bell of said clutch.
 5. Adrive assembly as claimed in claim 1, characterized in that saidelectric machine is reversible.
 6. A drive assembly as claimed in claim1, characterized by comprising an electric generator driven by saidinternal combustion engine.
 7. A drive assembly as claimed in claim 1,characterized by comprising a control unit for controlling said internalcombustion engine and said electric machine, in response to a number ofinput signals (Se, Sf, Ss), in a number of operating modes comprising atleast a combustion mode wherein only the internal combustion engine isactivated, an electric mode wherein said electric machine operates as amotor and said internal combustion engine is disabled, a parallel hybridmode wherein said internal combustion engine and said electric machineare both activated and connected to said drive wheel, and a serieshybrid mode wherein said internal combustion engine is disconnected fromsaid drive wheel and drives said electric generator.
 8. A drive assemblyas claimed in claim 7, characterized by comprising selecting means forselecting said operating modes of said drive assembly; said inputsignals (Sa, Sf, Ss) comprising at least a number of input signals (Ss)generated by said selecting means.
 9. A drive assembly as claimed inclaim 7, characterized in that said input signals (Sa, Sf, Ss) comprisea signal (Sa) indicating the position of an accelerator member.
 10. Adrive assembly as claimed in claim 7, characterized in that said inputsignals (Sn, Sf, Ss) comprise a signal indicating actions on a brakecontrol member of the vehicle.
 11. A vehicle having at least one drivewheel, characterized by comprising a hybrid drive assembly as claimed inclaim
 1. 12. A vehicle as claimed in claim 11, characterized by being ascooter.